Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $164.53   10.300%   $181.4766   $181.48   $181.50   $181.50  
  Purchase #2 $99.46   12.250%   $111.6439   $111.64   $111.65   $111.60  
  Purchase #3 $184.83   10.828%   $204.8434   $204.84   $204.85   $204.80  
  Purchase #4 $167.66   3.643%   $173.7679   $173.77   $173.75   $173.80  
  Purchase #5 $20.58   11.616%   $22.9706   $22.97   $22.95   $23.00  
  Purchase #6 $241.36   7.252%   $258.8634   $258.86   $258.85   $258.90  
  Purchase #7 $197.35   8.278%   $213.6866   $213.69   $213.70   $213.70  
  7 purchase totals = $1,075.77       $1,167.2524   $1,167.25   $1,167.25   $1,167.30